I’ve been trying to get people to encrypt their email, and send me encrypted email, since 1995 or so. Here’s why: email is cleartext.
What does “cleartext” mean?
Well, if your ISP is having you send your email out through port 25, you can do this. (I’ve done it myself to test my own mail server at work.)
That’s basically what happens, automated, when you send your email out through a client. So unless your ISP has you send your mail out over SSL (they’ll probably give you another port to use, like 465 or 587), anyone sitting between you and your ISP’s outgoing mail server can potentially sniff that mail. (Like, that malicious person at the free wifi hotspot you’re using.)
So, you have an encrypted connection to your outgoing server, or you’re using https to access webmail. YAY! People sitting between you and that server can’t sniff it.
(Note: It’s even worse if you aren’t encrypting the connection to your incoming mail server in a mail client. Your username and password are sent cleartext over the wires.)
Don’t relax yet. 😉
What happens next is that your outgoing mail, or SMTP, server goes through the same process with your recipient’s SMTP server. This connection may or may not be encrypted and you have no way of knowing this unless your ISP refuses to talk to other servers that don’t encrypt. (Posteo.de says they do that.) Then the mail is stored on a server disk unencrypted until you or the recipient access it.
This is where encrypting the contents come in. If I send someone an encrypted email, my outgoing mail server and their incoming mail server know that:
- the mail came from my email address
- the mail is addressed to their email address
- there is a cleartext subject line.
The contents, however, look like:
—–BEGIN PGP MESSAGE—–
Version: GnuPG v2
—–END PGP MESSAGE—–
By the way, even though I’ve posted that to my blog, only the person who has the private key can read that.
This isn’t new technology. It’s actually old. The reason everyone isn’t using it is because it’s not set up by default, and because the people you email are probably not using it already and you can’t if they don’t. 🙁
If you’re a webmail user, there’s Mailvelope, which I haven’t used. For everyone else, Enigmail for Thunderbird is awesome. GPG4Win used to be kind of buggy but it’s gotten really good–I particularly like the “encrypt/decrypt clipboard” feature, which I’m using instead of Mailvelope for webmail.
Then, all you need is a recipient’s public key. (You always encrypt to the recipient’s public key.) The way it works, in short, is that each person has two keys: one public, one private. They give the public key to you and keep the private one a secret. Only the private key can decrypt something encrypted with its public key. So only one person can read what you’ve sent, and that’s the person who’s got the private key. (Here’s more.)